The ability of apelin to reduce arrhythmia vulnerability in isolated exercised atria was associated with prolongation (~17%, P < 0.001) of action potential duration at 80% of repolarization (APD80) (Figure 2K), which was also observed in atria isolated from sedentary control mice (in which atrial arrhythmias cannot be induced) (~13%, P < 0.001). This evidence concerns the gene APLN and cardiac arrhythmia.